1. Field of the Invention
The present invention relates to a thermoplastic polymer composition with good melt adhesiveness, a laminate containing a layer of the composition, and a hot-melt adhesive including the composition. More precisely, the invention relates to a thermoplastic polymer composition with high flexibility, high elasticity, and good mechanical and adhesive properties.
2. Description of the Prior Art
Recently, block copolymers composed of styrenic polymer blocks and dienic polymer blocks (hereinafter referred to as "styrene-diene block copolymers") and their hydrogenates have been widely used in various fields as one type of so-called thermoplastic elastomers. They exhibit rubber elasticity at room temperature but may be plasticized and melted under heat to give shaped articles that are both flexible and have good mechanical properties.
A typical application for thermoplastic elastomers is a laminate composed of a layer of such a styrene-diene block copolymer and/or its hydrogenate, and a layer of hard resin and/or metal. These laminates are desirable as high value-added products, since they have a good feel, shock absorption (cushionability) and damage-resistance because of the flexibility and elasticity of the layer of the styrene-diene block copolymer and/or its hydrogenate; and the shape-retaining functions, reinforcing ability and fixing functions of the hard resin and/or metal layer. Various parts of cars and trains are envisaged for these materials such as instrument panels, center console boxes, door trims, pillars and assist grips as well as construction materials such as doors and window frames, various parts of electric appliances such as switches and grips, plaster casts for medical use, etc.
Being relatively non-polar, styrene-diene block copolymers and their hydrogenates can be melt-adhered to or melt-integrated with relatively non-polar plastics which are similar in kind, but which are difficult to melt-adhere to highly-polar plastics and metals. Accordingly, when laminated with highly-polar materials to give composites, mechanical coupling methods must be employed in which both a layer (part) of styrene-diene block copolymer and/or its hydrogenate and a layer (part) of plastic and/or metal are formed to have engaging means capable of being coupled together, and they are coupled together at their engaging means. Alternatively, the two layers (parts) are bonded together with some other bonding means, such as chemical bonding methods and adhesives.
However, the mechanical coupling methods where the two layers (parts) are formed to have couplable engaging means require molds with complicated structures for forming those means. The formation of such molds takes a lot of time and labor, which increases the production costs. In addition, coupling of the two engaging means requires complicated operations.
The use of adhesives is also undesirable because it requires complicated steps to prepare the two layers (parts) followed by bonding. As a result, poorly-bonded composites are often produced, and organic solvents in adhesives often are detrimental in the working environment and in the global environment.
Given that situation, various techniques for improving the hot-melt adhesiveness of thermoplastic elastomers of styrene-diene block copolymers and/or their hydrogenates have heretofore been proposed. As the prior art, for example, known are (1) adhesive hot-melt compositions comprising a styrene-diene block copolymer or its hydrogenate and a thermoplastic polyurethane elastomer (see Japanese Patent Application Laid-Open No. 6-107898), (2) thermoplastic elastomer compositions comprising a thermoplastic elastomer other than thermoplastic polyester elastomers and a thermoplastic polyester elastomer (see Japanese Patent Application Laid Open No. 3-100045), and (3) olefinic elastomer compositions comprising at least one thermoplastic elastomer selected from hydrogenated styrene-diene block copolymers and ethylene/.alpha.-olefin copolymers, and an ethylene-alkyl (meth)acrylate random copolymer (see Japanese Patent Application Laid-Open No. 7-138418).
However, the prior art compositions of (1) do not have good adhesion strength, depending on the type of the materials to be laminated with the compositions, and the resulting laminates (composites) do not always last long. In addition, since the melt dispersion of the styrene-diene block copolymer or its hydrogenate and the thermoplastic polyurethane elastomer is poor, the compositions comprising these two components are often poorly dispersed blends having large grain sizes. Therefore the shaped articles of the compositions do not have good mechanical properties.
The prior art compositions of (2) also do not have good adhesion strength, depending on the type of the materials to be laminated with the compositions, and the resulting laminates (composites) do not always last long. The shaped articles of these compositions release poorly from the molds and dies used in melt-molding them, for example, through injection molding. As a result, the reproducibility of the articles is poor.
In addition, the prior art compositions of (1) and (2) have poor weather resistance. Therefore, the laminates comprising them could not be used in the open air, and their applications are limited.
The prior art compositions of (3) exhibit poor miscibility between the thermoplastic elastomer and the ethylene-alkyl (meth)acrylate random copolymer. Therefore, the compositions comprising those two components are often poorly dispersed blends having large grain sizes, and the shaped articles of the compositions often have poor mechanical properties. In addition, when the compositions are melt-molded to give shaped articles, for example, through injection molding, the dispersed phases of the compositions will be further thickened due to the shearing force applied thereto during melt-kneading them, whereby the mechanical properties of the shaped articles are worsened.